1. Field of the Invention
The present invention relates to an apparatus for measuring the quality, such as internal sugariness or the like, of the greengrocery (fruits and vegetables) such as oranges, melons, watermelons, and so on on a non-destructive basis and, more particularly, to a processing circuit for processing initial data obtained by the measurement at higher speed and with higher accuracy.
2. Related Background Art
In general, the internal quality of the fruits or vegetables before shipping has been evaluated heretofore mainly by visual inspection of skilled inspectors. Certain fruits or vegetables, if harvested or shipped in a full ripe state, would undergo deterioration of taste, saccharification of sarcocarp, etc. on the market. Therefore, such fruits or vegetables are harvested in an unripe state and thereafter are made to stand under fixed temperature to effect afterripening into an edible state. It was also conventional practice to judge completion of the afterripening by visual inspection of inspectors as above, but it was difficult to make an accurate judgment, because there were no definite criteria for such evaluation of the internal quality of fruits or vegetables.
On the other hand, based on the fact that when near-infrared light is projected onto the fruits or vegetables, such components as sugars, acids, or the like in the fruits or vegetables absorb light of specific wavelengths, it is possible to know the internal quality, such as the sugariness or the like, of the fruits or vegetables by analyzing the light transmitted by the fruits or vegetables and there are known methods for determining the internal quality of the fruits or vegetables on a non-destructive basis, using the transmitted light of the near-infrared light.
Specifically, FIG. 13 is an example to show a schematic diagram of a measurement device for measuring the internal quality of the fruits or vegetables. In FIG. 13, inspected objects 5, which are the fruits or vegetables, are conveyed on a conveyor system 10, for example, such as a conveyor or the like, and in that state the internal quality of the inspected objects 5 is measured continuously. First, the existence of an inspected object 5 on the conveyor system is checked by a position sensor 11. Then a light source 1 radiates light having a predetermined frequency region (which will be referred to hereinafter simply as light) toward the inspected object 5 at a predetermined position A on the conveyor system. Among the radiated light, light of certain wavelengths is absorbed by sugars or the like existing in the inspected object 5 and thereafter the light is transmitted by the inspected object 5 to the outside. This transmitted light is measured by a light receiving element 2 and the transmitted light obtained by this measurement is analyzed in a signal processing device 12, thereby permitting us to know the internal quality of the inspected object 5.
In the practical evaluation of the internal quality of fruits or vegetables, however, the light used in the spectral analysis of fruits or vegetables has a wide frequency region and, in order to obtain the accurate internal quality by signal processing in practice, it is necessary to split the frequency region into a plurality of frequency regions and carry out the signal processing for each of the split frequency regions. Conceivable methods for the division and signal processing of the frequency region include methods of 1) and 2) described below.
1) Interference filters, each transmitting only light in a predetermined frequency region, are prepared in the number of their frequency regions equal to the number of split measurement frequency regions, the filters are continuously changed one by one at a light receiving portion of the light receiving element, so as to continuously send the transmitted light of the split frequency regions to the signal processing device, and the signal processing device carries out the signal processing therewith. One measurement operation for the measured frequency region is completed after the filters all have passed the light receiving portion.
2) For example, as described in Japanese Laid-open Patent Application No. 7-22984, a diffraction grating for separating measured wavelengths is placed at the light receiving portion, the transmitted light after split is guided to an array having storage-type sensors in the number according to the number of separate regions, and after completion of one measurement, data stored is successively subject to signal processing by a single signal processing circuit (including an amplifier etc.).
Since the permissible time for the evaluation of quality in a grading process of fruits or vegetables is very short, the evaluation of fruits or vegetables under conveyance on the conveyor system has to be carried out continuously for the fruits or vegetables. However, since the internal quality of the fruits or vegetables varies considerably, depending upon measured regions thereof, the evaluation has to be carried out on a basis as continuous and in a range as wide as possible. For the accurate evaluation, sufficient light energy has to be accumulated with reception of the transmitted light.
In the case of the method of 1) described above, however, since the fruit or vegetable moves during switching of the interference filters, the measured regions are also shifted with the switching of the frequency regions and data for one frequency region out of the split frequency regions is discontinuous and partial in the measured region on the fruit or vegetable. Further, since the data obtained for the respective split frequency regions is one at different measured regions for the same reason, it is difficult to obtain the accurate measurement result of internal quality. The measurement time for each split frequency region becomes shorter and shorter as the number of split frequency regions increases. This would pose a problem that it is difficult to obtain the sufficient light energy of the transmitted light or the like.
In the case of the method of 2) described above, though the diffraction grating splits the transmitted light at one time, the data stored has to be sent serially from the array to the signal processing circuit. Therefore, data storage start times and storage end times for the respective split frequency regions are shifted in order according to the data transfer times. Since this temporal deviation in the data storage timing for each split wavelength is as small as ten and several msec, the problem of discontinuous measured regions on the fruit or vegetable or different measurement positions of data obtained for the respective split frequency regions, and the problem of decrease in the light energy stored per unit time are not so serious as compared with the case of the method of 1). This method was, however, inadequate in a sense of obtaining a more accurate measurement result of the internal quality of fruit or vegetable or in a sense of decreasing the permissible time for the measurement of quality. Further, this method needs a step of initialization to erase the data stored in each sensor on the array after completion of one measurement. This posed a problem in decreasing the time necessary for the measurement.
In the method 2) described above, a conceivable means for solving the above problem is an approach for increasing the storage time for each frequency region to several ten msec. In this approach, however, if during a certain period within the storage time abnormal intensity data appeared, for example, due to reception of external light other than the transmitted light on the light receiving element or due to the dust or the like attached to the fruit or vegetable, it was difficult to find out a profile of intensity data in the storage time and there was a possibility that the data including the abnormal value was used as it is.
Actual intensities of the transmitted light vary large depending upon the frequency regions and it is thus necessary to select an appropriate amplification factor on the occasion of the signal processing of stored data, set a base line according to the amplification factor, and then carry out the signal processing for calculating the internal quality. With decreasing the storage time, the number of signal processing operations and the number of initialization operations of each sensor also increased, which would raise the possibilities of increase of measurement errors caused by generation of heat due to increase of loads on the signal processing circuit and increase of the measurement time over the permissible time.
Further, in the practical evaluation of the internal quality of fruit or vegetable, the intensity of light through the inspected object 5 is very weak and it is thus necessary to eliminate influence of the external light except for the transmitted light present around the light receiving element 2. For that reason, the measurement system was placed in an unrepresented shield chamber capable of sufficiently intercepting the light from the outside of the apparatus. Further, a disk 8 having cutouts at a predetermined period on the circumference was located between the light source 1 and the inspected object 5, and the disk 8 was rotated by a motor 9 to change the light to pulsed light having the predetermined period. Then the signal processing was carried out with only the pulsed light, thereby eliminating the influence of external light.
In some cases, when the light radiated toward the inspected object 5 is received by the light receiving element 2, it includes not only the transmitted light passing through the inside of the inspected object 5, but also the other light than the transmitted light, resulting from reflection from other inspected objects conveyed before and after the inspected object 5 of interest or resulting from scattering, reflection, etc. due to the dust floating in the measurement system and particles etc. carried into the measurement system by the inspected objects 5 (such light will be referred to hereinafter as stray light). In order to eliminate this influence, the conventional countermeasures contemplated include a method for accommodating the inspected object 5, for example, in a bored shield basket and receiving the transmitted light through the bore, and the like.
The evaluation, however, has to be carried out with effecting high-speed conveyance in order to raise the efficiency of the evaluation of internal quality of fruits or vegetables, and the time necessary for the evaluation has to be decreased thereby. In this case, where the pulsed light is obtained by the aforementioned method, for example, stable operation of the motor 9 is required, but there is the limit in increasing the number of rotations. Even if the pulsed light is obtained by another method, the energy of the light received by the light receiving element 2 will be decreased because of the conversion to the pulsed light. It is, therefore, necessary to increase the energy of the light received in order to obtain the evaluation result with high accuracy.
Further, there recently also occurred some cases where it was difficult to receive the light in sufficient energy for obtaining the intensity data in order to know characteristics of the object unless non-pulsed light was used, depending upon the measured substance of the internal quality. In order to eliminate the influence of the external light without use of the pulsed light, it is effective to enhance the shield performance of the apparatus from the external light, but it increases the size of the apparatus. Therefore, there is the practical limit. Further, the stray light reaching the light receiving element could also increase if the intensity of the light radiated were increased in order to increase the energy of light.
In the actual measurement the internal quality of fruit or vegetable differs greatly depending upon measured regions, and the evaluation of internal quality thus has to be carried out in an area as large as possible. The size of the fruits or vegetables, however, differs considerably even in a single kind. It is thus preferable in practice to carry out the evaluation of internal quality with changing the measurement area according to each inspected object. The enlargement of the measured portion, however, could also increase the influence of the stray light at the same time.
A method for increasing the light energy is one for, with enhancing the shield state of the apparatus from the external light and increasing the intensity of radiated light, for example, splitting the transmitted light into a plurality of frequency regions by the diffraction grating or the like, receiving the transmitted light thus split, using storage-type line sensors or the like as light receiving elements, and, after a lapse of a predetermined time, obtaining the evaluation result by use of the stored data. This method can also further decrease the influence of the external light which has already been weakened by carrying out the initialization of each sensor every appropriate measurements. This method, however, would raise the possibility that when the light receiving element receives instantaneous stray light due to the particles or the like as described above, data is stored also including the stray light, thus failing to obtain an accurate evaluation result.
Even with use of the bored shield basket, the shape of fruits or vegetables is not fixed and it is thus difficult to completely eliminate the gap between the hole of the shield basket and the fruits or vegetables. This becomes more prominent in the case of high-speed conveyance. Therefore, sufficient removal of the stray light cannot be achieved by this method.
Further, in the actual evaluation of the internal quality of fruit or vegetable, the size or absorbance of the inspected objects 5 differs depending upon the individual inspected objects even in the evaluation of the internal quality of fruits or vegetables of a specific kind. It is, however, common practice to determine the internal quality of a fruit or vegetable with the transmitted light through the fruit or vegetable, based on a rate of absorbance of a specific wavelength according to the internal quality in the transmitted light. It is, therefore, possible to evaluate the quality with only the transmitted light from one inspected object and it is virtually possible to derive the evaluation result even if the sizes or transmittances of the individual objects are different.
However, for example, where the fruits are oranges, the differences in the size of the individual oranges, even of a single kind, would cause intensities of the transmitted light to vary by differences of two or more figures in intensity ratios thereof in practice. In general, it is necessary to raise the S/N ratios (ratios of signal to noise) for the accurate intensity analysis every wavelength. It was, however, difficult always to obtain the accurate measurement result of internal quality of all the oranges, i.e., the fruits or vegetables of the same kind, because the differences in the intensities of the transmitted light were too large among the oranges, as described previously.
Further, with a single fruit or vegetable, intensities are also often considerably different among the wavelengths. If a signal amplification factor was set in the signal processing device so as to obtain an accurate measurement result at a specific wavelength accurate evaluation could not be made at wavelengths different from the specific wavelength in certain cases.
In addition, the above-stated evaluation in the grading process of fruits or vegetables normally has to be carried out in a state in which they are conveyed by a conveying system, for example, such as a belt conveyor. In this case, the inspected objects 5 are positioned at random on the belt conveyor and the permissible analysis time for each inspected object is very short. Under such measurement conditions, continuous projection of the near-infrared light from the light source 1 is effective in reducing the measurement time.
In this case, even with consideration to the aforementioned problems related to the signal processing, there, however, occur states in which the inspected object 5 is absent between the light source 1 and the light receiving element 2 during the conveyance, so that the near-infrared light is received directly by the light receiving element 2. As a consequence, there arose the possibility that the base line (a value as a reference of measurement) varied of measured values of the signal processing device 12 connected to the light receiving element 2 or that the signal processing performance was degraded by increase of the temperature or the like in the internal circuits of the signal processing device 12 because of occurrence of too large voltage.